1. Field of the Invention
The invention relates to a method of detecting an amplitude transient in a field of elements having a multivalent amplitude distribution by comparison of amplitude values of neighbouring elements on a search curve. The invention also relates to a device suitable for performing the method, and to a video system comprising such a device.
2. Description of the Related Art
A method and device of this kind are known from the data sheet "Plessey PDSP 16401 2-Dimensional Edge Detector", May 1986. This sheet describes a CMOS video signal processor for determining the presence, the direction and the magnitude of a gradient of an edge in a video image by multiplying each time a block of amplitude values of 3.times.3 pixels with four mask matrices. It is thus investigated whether an amplitude transient occurs in the horizontal, the vertical or the diagonal direction. The directions in which a search is made are referred to as search curves. Thus, in this case a search curve is chosen in the horizontal direction, the vertical direction and the diagonal direction. Each time an amplitude transient is searched along a search curve.
It is a drawback of such a method that the determination of the location of an edge is inaccurate: an edge is detected by way of a sufficiently large amplitude difference between neighbouring pixels. For example the sum of the amplitude values of three pixels, succeeding one another transversely to the search curve is compared with a corresponding sum formed by way of pixels located two pixels further along the search curve. If the difference between these sums is greater than a threshold value, the edge is situated at the pixels located between the two relevant threesomes of pixels, i.e. with an accuracy of 1 pixel.